ORLANDO, Fla. — A 12-year-old riding Walt Disney World's Rock 'n' Roller Coaster slumped over during the ride Thursday and later died, though his father performed CPR until paramedics arrived.

There was no indication why Michael Russell of Ft. Campbell, Ky., lost consciousness on the indoor roller coaster at Disney-MGM Studios, or why he died. The Orange County Sheriff's Office was investigating, and the medical examiner's office is to conduct an autopsy today.

The boy's parents, Byron and Charlotte Russell, and brother Houston, 7, were being assisted Thursday by park officials.

"Right now our deepest sympathies are with the family, and we are doing everything we can to assist them," said Disney spokesman Jacob DiPietri.

Byron Russell is a member of the Army's 5th Special Forces Group, stationed at Ft. Campbell.

The Russell family told deputies that Michael was in good health.

"There are no previous medical problems they know of," said Sheriff's Det. Mark Hussey, who was assigned to investigate. "He said his son had a yearly physical, the most recent just a few months ago."

Disney closed the ride and asked the Florida Bureau of Fair Rides Inspection to assist in an inquiry. There was no indication Thursday that equipment on the ride had malfunctioned.

State officials said Michael was the ninth person to die at Disney World since 2003. At least 15 people have died at Disney's theme parks in Florida and California since 1989.